This invention relates generally to valves, and more particularly to a through conduit gate valve having a slab gate member as the valve element and cooperating seat members which form a seal on both the upstream and downstream sides of the gate member.
Gate valves, particularly through conduit gate valves, which when open present an unbroken smooth wall conduit for uninterrupted passage of flow therethrough, are widely used because of their desirable flow characteristics. Generally, gate valves of the slab gate variety, are provided with two floating seats, so that as the gate moves across the conduit opening, the floating action of the gate and seats makes a total pressure-actuated seal which hold tight on both the upstream and downstream sides of the valve. However, in certain severe conditions, such as in geothermal applications where the effluent contains considerable amounts of minerals and foreign matter which tend to precipitate out to form sediment and scale deposits, the seats tend to become "frozen" in place by the formation of such precipitation. When this occurs, the seals are prevented from floating back into the seat pockets. Accordingly, when the valve is moved to the closed conditon, high contact loads are created between the gate and seats which may be assisted by shirnkage of valve components induced by temperature cooling changes as result in galling or scratching of the sealing surfaces and the requirement of a very high operating torque. Also, in applications with corrosive fluids, the back of the seat pocket becomes exposed to the corrosive fluid that may, in time, cause its deterioration to such a degree that the elastomer seals of the seat assembly will no longer function.
It is a primary object of the invention, therefore, to provide a gate valve with seat assemblies and seat pockets provided therefor which are protected from the debilitating effects of corrosive and fouling fluids ladings.
It is another object to provide a gate valve of the slab gate variety having floating seats for establishing upstream and downstream seals wherein the seat pockets are protected from solids depositions and accumulations and excessive pressure build-up behind the seats as would impair the operation of the valve.